Hi There,
Thanks for writing in! Is your X|theme is in latest version (4.6.4)? If not, you need to update that.
I was able to download a child theme from your “legacy” child themes and install 5 different versions.
That is the child theme for old x|theme. Please download the latest child theme here, you’ll get a x-child.zip file and install that like a normal theme.
Provide us login credentials in private reply, if you need further assistance on this.
Cheers!